diff --git a/sources/core/check.cpp b/sources/core/check.cpp
new file mode 100644
index 0000000..efa33b3
--- /dev/null
+++ b/sources/core/check.cpp
@@ -0,0 +1,45 @@
+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   check.cpp                                          :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: rparodi <rparodi@student.42.fr>            +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2025/05/13 11:25:04 by rparodi           #+#    #+#             */
+/*   Updated: 2025/05/13 11:59:01 by rparodi          ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+#include "core.hpp"
+#include <cerrno>
+#include <cstdlib>
+#include <iostream>
+
+/**
+ * @brief function to check if the port is valid
+ *
+ * @param input input given bu the user
+ * @return value between 1 and 65535 if valid, 0 if not
+ */
+unsigned short int valid_port(char *input)
+{
+	if (input == NULL)
+		return (0);
+	for (size_t i = 0; input[i]; i++) {
+		if (!isdigit(input[i])) {
+			if (DEBUG)
+				std::cerr << LOG << CLR_RED << "Error: Not only number in port: " << input << std::endl;
+			return (0);
+		}
+	}
+	errno = 0;
+	int port = strtol(input, NULL, 10);
+	if (errno == ERANGE) {
+		if (DEBUG)
+			std::cerr << LOG << CLR_RED << "Error: Port out of range: " << input << std::endl;
+		return (0);
+	}
+	if (port < 1 || port > 65535)
+		return (0);
+	return (port);
+}